The invention relates to apparatus for filtering solid particulate matter from fluids and, in particular, to improved filters formed from thin, porous walled honeycomb structures and means for mounting the filters for advantageous operation.
The removal of solid particulate matter from fluids (gases or liquids) in which they are mixed is typically accomplished by means of filters made from solid materials formed into articles or masses and having a plurality of pores (which may be interconnected) extending through them of a small cross-sectional size such that the solid materials are both permeable to the fluids and capable of restraining all or at least a substantial portion, as desired, of the solid particulate matter carried by the fluid from passing through the article or mass. Such pores constitute what is termed "open porosity" or "accessible porosity". The minimum cross-sectional size of some or all of the pores can be larger than the size of some or all of the particulates to be filtered, but only to the extent that all or significant amounts of sufficiently large particulates become trapped on the inlet surfaces and/or within the pores during the transit of the fluid through the article or mass.
A pending application Ser. No. 165,646, filed July 3, 1980, assigned to the assignee of this application, describes honeycomb filters preferably formed from extruded and sintered ceramic materials which may be used for removing carbonaceous particulates from diesel engine exhaust gases and for other high temperature fluid filtering applications. The filters are of honeycomb structure each comprising a matrix of thin, porous interconnected walls which define inlet and outlet end faces on opposing outer walls of the filter and a plurality of hollow passages or cells which extend through the filter body between the inlet and outlet end faces. The thin, porous cell walls may form the outer wall of the filter body between the end faces but more typically, a somewhat thicker, smooth continuous outer wall or skin is provided surrounding the matrix of thin walls for strength, uniform outer dimensioning, etc.. One end of each of the cells is blocked to form groups of inlet and outlet cells, the cells of the inlet group each being open at the inlet end face and blocked near the outlet end face and the cells of the outlet group each being blocked near the inlet end face and open at the outlet end face. The inlet and outlet cells are alternated in a checkered fashion so as to adjoin one another and share in common the thin porous walls which define each of the cells. A contaminated fluid introduced under pressure to the inlet end face passes into the filter body through the inlet cells and is forced across the narrow dimension of the thin porous walls, which trap the solid particulates present in the fluid, into adjoining outlet cells through which the now cleansed fluid exits the filter body. At least a substantial portion of the particulates are deposited on the thin wall surfaces of the inlet cells or are trapped in the pores within these walls.
Various methods have been employed to increase the capacity of a filter of given honeycomb geometry. One method described and claimed in a copending application Ser. No. 350,995 filed on the same date as this application and assigned to the assignee hereof, is to provide a filter formed from a matrix of thin, porous interconnected walls having interconnected open porosity of a volume and size sufficient to enable fluid to flow through the thin walls in both their narrow and longer dimensions between adjoining and/or neighboring inlet and outlet cells while preventing at least a substantial portion of the solid particulates in the fluid from flowing entirely through or across the thin walls in any direction and to additionally asymmetrically allocate the thin wall surface areas to provide greater collective inlet cell than outlet cell thin wall surface areas. In yet another pending application Ser. No. 351,126 filed on the same date as this application and assigned to the assignee hereof, a filter was provided for moderately high temperature use having a porous outer wall or skin surrounding the filter's matrix of thin walls and extending between its end faces and was mounted for use so as to enable fluid to flow across the thickness (i.e. narrow dimension) of the skin over a substantial portion of its surface area thereby reducing the likelihood of thermal gradients being formed near the skin and in the peripherally located cells of the filter. The invention also had the effect of increasing the filtration surface area of the filter and its particulate capacity.